Precious metal mobility during serpentinization and breakdown of base metal sulphide

Lawley, C J M; Petts, Duane C.; Jackson, Simon E.; Zagorevski, A; Pearson, D. Graham; Kjarsgaard, Bruce A.; Savard, Denis; Tschirhart, V

doi:10.1016/j.lithos.2019.105278

Cited by 25 publications

(22 citation statements)

References 60 publications

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“…The mapping procedure closely follows the method of Lawley et al. (2015, 2020). Elemental maps were constructed by rastering a focused laser beam across the sample surface to form a series of line scan ablations.…”

Section: Methodsmentioning

confidence: 99%

Major and trace element mapping of garnet: Unravelling the conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Gaidies

Morneau

Petts

et al. 2020

Journal Metamorphic Geology

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Garnet crystallization has been simulated in the MnNCKFMASHT model system using a simple nucleation and growth scenario, calibrated with three‐dimensional garnet crystal size distribution data as well as garnet compositional data obtained by electron probe micro‐analysis and laser ablation inductively coupled plasma mass spectrometry. Results indicate wide‐spread Barrovian‐type metamorphism for garnet‐zone rocks from the Snowcap assemblage along a hairpin‐shaped pressure–temperature loop with garnet growth from ~515°C and 4 kbar to metamorphic peak conditions of ~600°C and 6 kbar. Lu–Hf garnet‐whole geochronology points to initial garnet growth at c. 192.2 ± 4.7 Ma. Sm–Nd garnet–whole‐rock geochronology applied to a sample with garnet rims enriched in Sm indicates that the metamorphic peak conditions have been attained at c. 172.9 ± 2.4 Ma. Older garnet growth at c. 245.3 ± 0.8 Ma during a low‐P–high‐T event has been preserved as garnet cores separated from the Jurassic garnet rims by a sharp microstructural and compositional discontinuity. These polyphase garnets are restricted to Mn‐rich metapelitic lithologies. Trace element zoning in the outermost ~50 μm thin segments of the Early Triassic garnet cores reflects a short garnet growth episode in the presence of melt at peak conditions of ~710°C and 2.5 kbar, supported by phase equilibrium and diffusion geospeedometry calculations. Diffusion simulations across the interface between the Early Triassic garnet core and the Jurassic garnet rim indicate that the Barrovian‐type metamorphism during the Jurassic lasted for 20–25 Myr, in line with the radiometric data.

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Section: Methodsmentioning

confidence: 99%

Major and trace element mapping of garnet: Unravelling the conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Gaidies

Morneau

Petts

et al. 2020

Journal Metamorphic Geology

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“…LA-ICP-MS trace element maps were produced on central cross-sections of the largest garnets in 28HF18 and 45HF18, using a Photon Machines Analyte Excite 193 nm excimer laser coupled with an Agilent 7700x ICP-MS at the University of Ottawa (Canada). The mapping procedure closely follows the method of Lawley et al (2015Lawley et al ( , 2020. The energy of the laser was 4.5 J/cm 2 , the repetition rate was 30 Hz, and the He-flow rate was 1 L/min.…”

Section: Laser Ablation Inductively Coupled Plasma Mass Spectrometrymentioning

confidence: 99%

Testing the equilibrium model: An example from the Caledonian Kalak Nappe Complex (Finnmark, Arctic Norway)

Gaidies

Heldwein

Yogi

et al. 2021

Journal Metamorphic Geology

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The equilibrium model has been tested using Barrovian garnet-zone micaschists of the Kalak Nappe Complex. In our model, equilibrium in the MnNCKFMASHT system was established across the entire rock volume during prograde metamorphism except for garnet, which developed growth zoning preserved at levels controlled by the kinetics of intracrystalline diffusion. The preservation potential of the disequilibrium fluctuations required for nucleation of garnet has been considered in our simulations, using a moving boundary multicomponent diffusion and growth model. Results indicate that the core of garnet that crystallizes during regional metamorphism does not retain the major element composition of the nucleus but reflects the compositional signature of the immediate overgrowth. The differences between the metamorphic conditions of successive garnet growth steps of the samples indicate characteristic trends in their pressure-temperature evolutions that can be predicted with the equilibrium model. There is some latitude with regard to the absolute metamorphic conditions due to the inherent uncertainty of the thermodynamic data and the approximation of the reactive volume composition. However, the slopes of the pressure-temperature paths together with systematic trends in the lithological, geochemical, and Lu-Hf garnet whole-rock isotopic properties of the rocks, as well as their garnet crystal size frequency distributions, enable the identification of the Veidnes, Bekkarfjord, and Kolvik Nappes involved in the Caledonian Orogeny and provide new insight into their metamorphic evolutions. According to our findings, the base of the Kalak Nappe Complex experienced wide-spread Barrovian-type metamorphism at c. 420 Ma with a gradient of $40 bar/ C and peak conditions of $560 C and 6.7 kbar in the Bekkarfjord and Veidnes Nappes, whereas the hinterland-placed Kolvik Nappe was metamorphosed at peak conditions of $590 C and 7.5 kbar. This event was preceded by moderate-pressure metamorphism at c. 423 Ma resulting in garnet crystallization exclusively in the Bekkarfjord Nappe, along a gradient of $20 bar/ C and peak conditions of $570 C and 6.0 kbar. We consider both of these metamorphic and deformational episodes to be different

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Section: Formation Of Au-bearing Compounds In Mineralized Volcanic Systemsmentioning

confidence: 99%

“…Lawley and co-authors proposed that base metal sulfides also carrying substantial quantities of gold and platinum-group elements (PGE) become unstable during serpentinization of sulfide-bearing ultramafic rocks [125]. Under this scenario, Au, Ag, Pt and Pd partition into intermetallic compounds, when sulfides are replaced by metal alloys and native metals during serpentinization [125]. Co-existing base metal sulfides (chalcopyrite, bornite, pentlandite) and gold-bearing alloys (as well as native gold in some cases) have been reported from peridotites [28,126,127] and subduction-related ultramafic rocks [38,39,128].…”

Section: Formation Of Au-bearing Compounds In Mineralized Volcanic Systemsmentioning

confidence: 99%

Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

et al. 2021

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While gold partitioning into hydrothermal fluids responsible for the formation of porphyry and epithermal deposits is currently well understood, its behavior during the differentiation of metal-rich silicate melts is still subject of an intense scientific debate. Typically, gold is scavenged into sulfides during crustal fractionation of sulfur-rich mafic to intermediate magmas and development of native forms and alloys of this important precious metal in igneous rocks and associated ores are still poorly documented. We present new data on gold (Cu-Ag-Au, Ni-Cu-Zn-Ag-Au, Ti-Cu-Ag-Au, Ag-Au) alloys from iron oxide deposits in the Lesser Khingan Range (LKR) of the Russian Far East. Gold alloy particles are from 10 to 100 µm in size and irregular to spherical in shape. Gold spherules were formed through silicate-metal liquid immiscibility and then injected into fissures surrounding the ascending melt column, or emplaced through a volcanic eruption. Presence of globular (occasionally with meniscus-like textures) Cu-O micro-inclusions in Cu-Ag-Au spherules confirms their crystallization from a metal melt via extremely fast cooling. Irregularly shaped Cu-Ag-Au particles were formed through hydrothermal alteration of gold-bearing volcanic rocks and ores. Association of primarily liquid Cu-Ag-Au spherules with iron-oxide mineralization in the LKR indicates possible involvement of silicate-metallic immiscibility and explosive volcanism in the formation of the Andean-type iron oxide gold-copper (IOCG) and related copper-gold porphyry deposits in the deeper parts of sub-volcanic epithermal systems. Thus, formation of gold alloys in deep roots of arc volcanoes may serve as a precursor and an exploration guide for high-grade epithermal gold mineralization at shallow structural levels of hydrothermal-volcanic environments in subduction zones.

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Precious metal mobility during serpentinization and breakdown of base metal sulphide

Cited by 25 publications

References 60 publications

Major and trace element mapping of garnet: Unravelling the conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Major and trace element mapping of garnet: Unravelling the conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Testing the equilibrium model: An example from the Caledonian Kalak Nappe Complex (Finnmark, Arctic Norway)

Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

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